Surface plasmon resonance (SPRS) is an optical phenomenon that occurs when light is cast at a certain angle onto a prism that has upon one surface a thin layer of conductive coating. The coating could comprise of one or more conductive or dielectric layers. When the light is shined into the prism at a particular “critical angle,” the light may totally internally reflect within the prism so that it does not escape that side of the prism. The critical angle depends upon the characteristics of the prism, the layer(s), or the environment surrounding the entire structure. This is caused by the interaction between light or other electromagnetic radiation and several different types of materials, usually comprising a dielectric material and a conductive material arranged in a multi-layer stack of thin films. Light that totally internally reflects within a coated prism forms an electromagnetic wave that propagates along the conductive (i.e., metal) layer boundary. This wave is known as a surface plasmon. The surface plasmon wave is optically excited at the interface between a conductor or semiconductor, e.g., a metal surface and a dielectric. For excitation of these surface plasmons a light source is needed.
Surface plasmon resonance spectroscopy (SPRSS) is a unique optical surface sensing technique with applications in a variety of disciplines. SPRS can be used to probe refractive index changes that occur within the immediate vicinity of a sensor surface. Thus, any physical phenomenon which alters the refractive index will elicit a response. Initial applications of SPRS involved the investigation of optical properties inherent to thin metal films. From these studies, SPRS has expanded and is used in of variety of applications including: absorbance measurements, biokinetic and biosensing techniques, bulk liquid measurements, gas detection, immunosensing, light modulation, process analytics, spectrometers, SPRS microscopy, refractive index measurements, SPRS polarization fibers, and thin film characterization. In recent years, the development of SPRS has been directed toward biosensing techniques. However, SPRS has not been limited to this field, for it has been used extensively in electrical engineering, chemistry, theoretical physics, and experimental optics.
Surface plasmon Resonance spectroscopy is a powerful technique to measure biomolecular interactions in real-time in a label free environment. While one of the interactants is immobilized to the sensor surface, others are free in solution and pass over the surface. Association and dissociation between the immobilized and free interactants is measured in arbitrary units and displayed in a graph called the sensorgram. Biomolecular Interaction Analysis is applicable to a variety of molecular pairs including interactions between DNA-DNA, DNA-protein, lipid-protein and hybrid systems of biomolecules. Non-biological surfaces can also be investigated.